In Javascript, when is it necessary to assign a named function to a variable?

Question

In the online REPL of Babel JS (http://babeljs.io/repl/), when I type in :

let a = (x) => x+1

It will be transpiled to:

Answer 1

If you write:

function a(x) { }

then the function is hoisted to the top of the enclosing scope, and a becomes available immediately at parse time within the entire scope.

However, when you write:

var a = function a(x) { }

then var a will not have a defined value in the enclosing scope until this line is actually executed.

However, within that function, a different a will exist as a locally scoped reference to the function itself.

By using the let a = function ... construct Babel is being more consistent with the latter form, ensuring that a is assigned at run time to a (named) function expression instead of using a parse time function declaration.